Spark plug with combined high tension gap and creepage spark gap



April 11, 1967 o. BEESCH SPARK PLUG WITH COMBINED HIGH TENSION GAP AND CREEPAGE SPARK GAP Filed Sept 16 1965 FIG. I

United States Patent Ofifice 3,313,972 Patented Apr. 11, 1967 3,313,972 SPARK PLUG WHTH CUMBINED HKGH TENSKQN GAP AND (IREEPAGE SPARK GAP Otto Becsch, Stuttgart-Sonnenherg, Germany, assignor to Robert Bosch G.rn.h.H., Stuttgart, Germany Filed Sept. 16, 1965, Ser. No. 487,881 Claims priority, application Germany, Get. 7, 1964, B 7 8,825 9 Claims. (Cl. 313-130) The present invention relates to a spark plug with combined high tension and creepage spark gap in which in order to lengthen the spark gap for the sparks between the center electrode and the ground electrode of the spark plug, a face of the insulator means separating the ground electrode from the center electrode is located in the path of the sparks between center and ground electrode so that the sparks will slide along part of their path between the center and the ground electrode along the aforementioned face of the insulator.

Combined spark gaps of the aforementioned kind require a smaller ignition voltage while having a better ignition efficiency than spark plugs having only a high tension spark gap. In spark plugs of the aforementioned kind there exists, however, the danger that the spark creeping along the face of the insulator burns a path in the insulator so that the latter cracks due to thermal overload and breaks oil producing thereby :aninterruption of the sparking path so that the spark plug is not useable any longer.

It is an object of the present invention to overcome this disadvantage of spark plugs of the aforementioned kind.

It is an additional object of the present invention to provide for a spark plug of the aforementioned kind which will operate satisfactorily even if part of the insulator forming the high tension and creepage spark gap should be destroyed.

It is a further object of the present invention to provide a spark plug of the aforementioned kind which is composed of relatively few and simple parts so that the spark plug can be manufactured at reasonable cost and will stand up troublefree under extended use.

With these objects in view the spark plug according to the present invention with a combined high tension and creepage spark gap mainly comprises a first electrode adapted to be connected at one end thereof to a source of high tension, a ground electrode spaced from the first electrode and having one end in the region of the other end of the first electrode, insulator means between the electrodes and having an end face in the region of the aforementioned one end of the ground electrode and in the path of sparks passing from the first to the second electrode, which end face is separated at least from one of the electrodes by an air gap forming with the end face a combined spark gap, whereby sparks between the electrodes will during part of the path slide along the end face, and means electrically connected to one of the electrodes and constructed and arranged to form an additional high tension spark gap with the other electrode of a length which is shorter than the total length of the combined spark gap. The additional high tension spark gap in the spark plug according to the present invention is arranged in parallel to the combined spark gap. The length of the additional high tension spark gap is dimensioned in such a manner that during normal operating conditions no sparking will occur through the additional high tension spark gap, and in such a manner that when the spark plug is cold and when for some reason no sparking should occur across the combined spark gap, sparking across the additional high tension spark gap will be assured as long as the necessary high tension is applied to the first electrode.

The novel features which .are considered :as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, bot-h as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a partially sectioned side view of one possible embodiment of a spark plug according to the present invention;

FIG. 2 is an end view drawn to an enlarged scale of an element of the spark plug shown in FIG. 1;

FIG. 3 is a partial view of an end portion of the spark plug shown in FIG. 1 drawn to an enlarged scale;

FIG. 4 is a partial sectional view of another embodiment of a spark plug according to the present invention; and

FIG. 5 is an end view of an element of the embodiment shown in FIG. 4.

Referring now to the drawings, and more specifically to FIGS. l-3 of the same, it will be seen that the embodiment of the spark plug 1 illustrated in these three figures includes a metal housing 2 which surrounds an insulator 5 and is held slightly spaced from the latter by means of a pair of axially spaced gaskets 3 and 4, an annular member or ring electrode 6 and a substantially L-shaped metal pin 7 projecting from the annular member 6. The ring electrode 6 and the L-shaped pin 7 form with the metal housing 2 a ground electrode relative to the center electrode 8. The ring electrode 6 is fastened to the lower end of the housing by a flange portion 14 at the end of the housing 2 pressed over the chamfered peripheral surface of the ring electrode 6, whereas one end of the L-shaped pin 7 is pressed into a corresponding bore formed in the lower end of the housing. The ring electrode 6 is formed, as best shown in FIG. 2, with a plurality of substantially circular cut-outs 15 extending from the inner periphery of the ring electrode 6 into the latter so as to leave between the cut-outs a plurality of edge portions 16 which are spaced radially outwardly a small distance from an end portion of reduceddiameter of the insulator 5 at the lower end of the spark plug 1. The ignition end of the center electrode 8 projects in axial direction beyond the ring electrode 6 and to avoid any tension in the insulator 5, the center electrode is provided at 10 with a tapering portion so that the lower projecting end of the center electrode has a smaller diameter than the remainder thereof. The head end 11 of the center electrode 8 is by means of a glass plug 12, anade electrically conductive by enclosed metal particles, connected to a connecting bolt 13 extending through a central bore of the insulator 5 and projecting with an end thereof distant from the center electrode 8 beyond the insulator 5. A contact bushing 13 screwed onto the outwardly projecting end of the bolt 13 serves to connect the latter to an ignition cable, not shown in the drawing, which in turn is connected to a source of high tension.

As can be seen from FIG. 3, the end face 9 of the insulator 5 is separated by an annular air gap L from the edge faces 16 of the ring electrode 6 and by an annular air gap L from the peripheral surface of the center electrode 8. The cut-outs 15 and the ring electrode 6 facilitate entrance of gases from the cylinder of a combustion engine in which the spark plug 1 is used into the space 17 above the ring electrode 6 which is essential for proper functioning of the spark plug.

During operation of the spark plug 1 and application of high tension to the center electrode 8 sparks will pass between the center electrode 8 and the edge portions 16 of the ring electrode 6 along the spark gap a indicated in dash-dotted lines in FIG. 3, whereby the sparks will pass through the air gap L slide along the end face 9 of the insulator 5 and pass through the air gap L so that the end face 9 forms with the air gaps L and L 2 combined spark gap through which the sparks pass during normal operation of the spark plug 1 from the center electrode 8 to the ring electrode 6 forming part of the ground electrode.

The free end of the L-shaped pin 7 facing the peripheral surface of .the center electrode 8 is spaced from the latter a distance which smaller than the length of the combined spark gap a, but slightly greater than the sum of the widths of the air gap's L and L :and the free end of the L-shaped pin 7 forms with the peripheral surface of the center electrode 8 an additional high tension spark gap b, which under normal operating conditions will not be bridged by sparks, but sparks will form through the spark gap 1) only when sparking through the combined spark gap a should cease, for instance after damage and breaking of the end of the insulator at which the end face 9 is formed.

FIG. 4 partially illustrates an additional embodiment of a spark plug according to the present invention. FIG. 4 shows only the lower portion 20 of this embodiment, and it is to be understood that the portion of the spark plug not illustrated in FIG. 4 is the same as in the embodiment illustrated in FIG. 1. The electrode arrangement of the embodiment illustrated in FIG. 4 differs from that shown in the preceding figures mainly by the specific construction of the annular metal disk 21 surrounding the center electrode l3 and serving as a ground electrode. The annular metal disk 21 is fastened to the lower end of the housing by means of a flange portion 24 of the latter bent over the outer peripheral surface of the annular disk 21. The inner peripheral surface 23 of the annular metal disk 21 which is interrupted by three tongues 22 projecting radially inwardly beyond the inner peripheral surface 23 surrounds the lower end of the insulator 5 radially spaced therefrom and defines the outer periphery of a combined spark gap constituted by the air gap between the surface portions 23 and the lower end of the insulator 5, the end face of the latter and the additional air gap between the inner periphery of the insulator 5 and the outer peripheral surface of the center electrode 18. The tongues 22 project with the inner free ends thereof beyond the inner peripheral surface portions 23 of the annular metal disk 21 and they are pressed at an angle out of the plane of the metal disk in such a manner that the free ends of the tongues 22 are spaced from the outer peripheral surface of the center electrode 18 a distance smaller than the peripheral surface portions 23 are spaced from the outer peripheral surface of the center electrode 18. The gaps 25 formed by bending the tongues 22 out of the plane of the disk 21 serve the same purpose as the cut-outs 15 in the ring electrode 6 shown in FIG. 2.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of a spark plug with combined high tension and creepage spark gap, differing from the types described above.

While the invention has been illustrated and described as embodied in a spark plug having a combined high tension and creepage spark gap and an additional high tension spark gap, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features which from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, sue-h adaptations should and are ind tended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A spark plug with combined high tension and creepage spark gap comprising, in combination, a first electrode adapted to be connected at one end to a source of high tension; at ground electrode spaced from said first electrode and having one end in the region of the other end of said first electrode; insulator means between said electrodes and having an end face in the region of said one end of said ground electrode and in the path of sparks passing from said first to said ground electrode, said end face being separated at least from one said elec trodes by an air gap forming with said end face a combined spark gap, whereby sparks between said electrodes will during part of the path slide along said end face; and means electrically connected to one of said electrodes and constructed and arranged to form an additional high tension spark gap with the other electrode of a length which is shorter than the total length of said combined spark gap, said additional high tension spark gap being arranged in parallel to said combined spark gap.

2. A spark plug with combined high tension and creepage spark gap comprising, in combination, a center electrode adapted to be connected at one end thereof to a source of high tension; a ground electrode at least partly surrounding said center electrode spaced therefrom and having an end in the region of the other end of said center electrode; insulator means between said electrodes and having an annular end face in the region of said one end of said ground electrode and in the path of sparks passing from said center electrode to said ground electrode, said end face being separated from each of said electrodes by an annular air gap and the annular air gaps separating said end face from said electrodes forming with said end face a combined spark gap, whereby sparks between said electrodes will during part of the path slide along said end face; and means electrically connected to one of said electrodes and constructed and arranged to form an additional high tension spark gap with the other electrode of a length which is shorter than the total length of said combined spark gap, said additional high tension spark gap being arranged in parallel to said combined spark gap.

3. A spark plug as set forth in claim 2, wherein the sum of the radial widths of said annular air gaps is smaller than the lengths of said additional high tension spark gap.

4. A spark plug as set forth in claim 2, wherein said other end of said center electrode projects beyond said one end of said ground electrode, and wherein said means forming said additional high tension spark gap include a substantially L-shaped metal pin connected at one end thereof to said one end of said ground electrode and projecting with the other end thereof toward said other end of said center electrode.

5. A spark plug as set forth in claim 4, wherein said end face of said insulator means is spaced farther from said other end of said center electrode than said one end of said ground electrode.

6. A spark plug as set forth in claim 4, wherein said ground electrode includes a housing, an annular member at said one end of said ground electrode fixed to said housing and having an inner periphery closer to the outer periphery of said center electrode than the remainder of said housing.

7. A spark plug as set forth in claim 6, wherein said annular member is formed with a plurality of angularly spaced cut-outs extending from its inner periphery in radially outward direction.

8. A spark plug as set forth in claim 2, wherein said other end of said center electrode projects beyond said one end of said ground electrode, and wherein said ground electrode includes an annular member at said one 5 6 end thereof having an inner periphery surrounding said 9. A spark plug as set forth in claim 8, wherein said end face of said insulator means radially spaced thereannular member includes a plurality of tongues angularly from and forming therewith said corn bined spark gap, spaced from each other. and wherein said means forming said additional high tension spank gap include at least one tongue pressed at 5 R f renc s Cited by the Examiner an angle out of the material of said annular member and UNITED STATES PATENTS projecting with the free end thereof beyond said inner periphery of said annular member toward said other end igi gzlf :8

of said center electrode and being spaced therefrom a distance smaller than the radial distance between said in- T T ner periphery of said annular member and the outer pe- 10 JAMES LAWRENCE Examiner ripheral surface of said center electrode. C. R. CAMPBELL, Assistant Examiner. 

1. A SPARK PLUG WITH COMBINED HIGH TENSION AND CREEPAGE SPARK GAP COMPRISING, IN COMBINATION, A FIRST ELECTRODE ADAPTED TO BE CONNECTED AT ONE END TO A SOURCE OF HIGH TENSION; A GROUND ELECTRODE SPACED FROM SAID FIRST ELECTRODE AND HAVING ONE END IN THE REGION OF THE OTHER END OF SAID FIRST ELECTRODE; INSULATOR MEANS BETWEEN SAID ELECTRODES AND HAVING AN END FACE IN THE REGION OF SAID ONE END OF SAID GROUND ELECTRODE AND IN THE PATH OF SPARKS PASSING FROM SAID FIRST TO SAID GROUND ELECTRODE, SAID END FACE BEING SEPARATED AT LEAST FROM ONE SAID ELECTRODES BY AN AIR GAP FORMING WITH SAID END FACE A COMBINED SPARK GAP, WHEREBY SPARKS BETWEEN SAID ELECTRODES WILL DURING PART OF THE PATH SLIDE ALONG SAID END FACE; AND MEANS ELECTRICALLY CONNECTED TO ONE OF SAID ELECTRODES AND CONSTRUCTED AND ARRANGED TO FORM AN ADDITIONAL HIGH TENSION SPARK GAP WITH THE OTHER ELECTRODES OF A LENGTH WHICH IS SHORTER THAN THE TOTAL LENGTH OF SAID COMBINED SPARK GAP, SAID ADDITIONAL HIGH TENSION SPARK GAP BEING ARRANGED IN PARALLEL TO SAID COMBINED SPARK GAP. 